1. Field of the Invention
The present invention relates to a medical implantable lead of the type adapted to be implanted into a human or animal body for monitoring and/or controlling of an organ inside the body, having a fixation means in a distal end that is adapted to fix the distal end of the lead to the organ, an electrode member in the distal end adapted to be in contact with tissue of the organ and receive and/or transmit electrical signals from and/or to the organ, and at least one electrically conducting coil, which includes one or more electrically conducting helical wires and that is adapted to connect the electrode member in the distal end with a monitoring and/or controlling device in a proximal end of the lead.
The invention also relates to a method for manufacturing of a medical implantable lead.
2. Description of the Prior Art
It is well known in the art to use a medical implantable lead of the above kind to monitor and/or control the function of an organ inside a human or animal body, for example to monitor and/or control a heart by means of a monitoring and/or controlling device in form of a pacemaker or cardiac defibrillator connected to the proximal end of the lead. The medical implantable lead is provided with at least one electrical conductor in form of a coil having one or more helically formed electrical conducting wires. The lead is, in its distal end, provided with one or more electrodes, adapted to be in contact with the tissue of the organ and connected to the one or more electrical conducting coils, for receiving and/or transmitting electrical signals from and/or to the organ. The electrodes can optionally be formed as a contact electrode that abuts against a surface of the organ, as a penetrating electrode that penetrates through a surface of the organ so as to become embedded within the tissue, or as a so-called indifferent electrode that is surrounded by body fluids such as blood.
Normally, such medical implantable leads are not considered to be compatible with Magnetic Resonance Imaging (MRI), i.e. persons or animals having such a lead implanted into the body, are excluded from being examined by MRI scanning. This is due to the fact that the electromagnetic field, that is generated during the MRI scanning, will induce a current in the conductor, which connects the one or more electrodes in the distal end of the medical implantable lead with the monitoring and/or controlling device in the proximal end of the lead. This induced current may cause heating in the electrode that is in contact with the tissue of the organ. If the heating is too high, there is a risk that this will cause damage to the tissue. However, the use of MRI scanning for diagnostics is growing extensively and an increasing number of the population, who have a lead implanted, would benefit from MRI scans. It is thus desirable to reduce any heating at or close to the lead tip to acceptable and safe levels.
It is known in the art to provide such medical implantable leads with an electrical shielding, in form of a tube of braided wires, which surrounds the coil and which in its proximal end normally is connected to the casing of the monitoring and/or controlling device. However, such shielded medical implantable leads are associated with several disadvantages. The braided shielding will give the medical implantable lead an increased thickness as well as increased rigidity, which normally is not desirable. Moreover, the braided shielding will considerably increase the cost for manufacturing the lead, since it will involve the provision of one additional component, which has to be mounted when assembling the lead. Also, it has appeared that such a braided shielding can not prevent the induction of electrical current to the coiled conductor in a degree that is sufficient to safely permit an individual, having an implanted lead to be exposed to a MRI scanning.